The present invention relates to an apparatus which is capable of detecting automatically a geometric distortion of an image on a screen of a CRT display device. This invention also relates to a high fidelity camera device free from dark current deviations and from sensitivity deviations.
As well known, a CRT direct viewing display device generates a geometric distortion having a pincushion-like shape (hereinafter, referred to as "the pincushion distortion" for short, when applicable) due to the principle of the electromagnetic deflection. In addition, a CRT projection display device further generates a geometric distortion having an approximately trapezoidal shape due to the oblique projection.
As well known, the display device has a built-in correction circuit which operates to eliminate those distortions. In this connection, the tendency of late years is that the circuit for correcting a geometric distortion in the CRT projection type display device employs a digital convergence circuit.
In the digital convergence circuit, a display screen is represented by approximately 10.times.10 (100 in total) matrix-like lattice points. In this connection, the accurate positional adjustment can be performed independently at every lattice point.
However, in the above-mentioned prior art, the detection of the positional deviation of each lattice point (the dislocation of each lattice point from the associated normal position) was carried out through eyes of a human being. It took about 20 seconds for one lattice point and 2,000 seconds for 100 lattice points, i.e., about 30 minutes for 100 lattice points in order to adjust the positional deviation of all the lattice points.
The above-mentioned time required for the positional adjustment was applied to the monochromatic display device, and therefore, in the case of the three-primary-colors color display device, it took about 90 minutes in order to adjust the positional adjustment of all the lattice points.
For the purpose of shortening the above-mentioned considerable time required for the positional adjustment in the manufacturing process, the experiments were performed such that 10.times.10 sets of photodetector arrays (or camera arrays) were arranged near the screen of the display device. Prior art adopting a camera array system is described in JP-B2-1-60996. However, since the camera array system is expensive and is difficult to be transported, the application thereof to the field service was thus difficult. In addition, the prior art apparatus was based on the principle which is established in the inside of the so-called Nyquist limit.